[jayd16]

Ah, you don't mean enforce a novice making a mistake, you mean ensure from a design purity perspective?

I don't think its true that you need requests to flow both ways. For example, if a downstream API needs more context from an upstream one, one solution is to pass that data down as a parameter. You don't need to allow the downstream services to independently loop back to gather more info.

[rco8786]

Again, it depends on the business case. Software is simply too fluid to be able to architect any sort of complex system that guarantees an acyclic data flow forever.